Radioisotopes are used in a variety of medical procedures. Some radioisotopes, typically characterized by one or more of short half-life, relatively shallow penetration depth and relative low radiation strength, are permanently implanted in a patient. Such radioisotopes are generally implanted using one or more implant needles with the radioisotopes encapsulated in small containers often referred to as seeds. In a typical procedure, a plurality of seeds are loaded into a plurality of implant needles and then ejected from the implant needle into the patient to form a three-dimensional array of seeds in a treatment area. Usually, the seed array is designed based on a pre-determined dose plan made by a medical professional.
In order to position the seeds at appropriate locations in the seed array, it is desirable to space the seeds apart from one another in the implant needles in order to provide appropriate spacing of the seeds in the treatment area. Thus, in a prostate cancer treatment method, 1-12 seeds are typically loaded into each implant needle along with a plurality of spacers to provide the desired spacing between seeds. It is preferable to allow customization of the number and/or length of spacers between seeds to provide greater flexibility in dose planning by allowing a larger variety of different spacing between seeds.
The loaded implant needles are positioned for insertion into the patient, for example, using a stand with an X-Y coordinate grid, and then inserted into the patient. The seeds and spacers are then ejected from the needle using a stylet as the needle is withdrawn from the patient in order to position the seeds at the desired location in the patient.
U.S. Pat. Nos. 4,086,914; 4,167,179; 5,242,373 and 5,860,909 and International application publication no. WO 97/22379 describe manual seed injector arrangements for brachytherapy using seed cartridges to supply the seeds directly to an implant needle specially adapted to mate with such cartridges or magazines.
Manual loading of implant needles just prior to insertion into a patient is undesirable for a variety of reasons. It is desirable to minimize potential exposure of hospital personnel to radioisotopes and thus manual loading of a large number of seeds at the time of treatment is undesirable. On the other hand, manual loading has the advantage that it provides more flexibility to the user to modify the dose plan at the time of implantation in order to provide the best possible treatment procedure for the patient and most economically efficient procedure for a hospital.
Some devices have been developed for loading seeds into implant needles. For example, U.S. Pat. No. 4,759,345 describes a radiation shielded seed loader for loading hand-implanted hypodermic needles. U.S. Pat. No. 5,906,574 describes a vacuum-assisted apparatus for loading radioactive seeds within a shielded container. U.S. Patent application publication no.: US 2002/0077521 A1 discloses methods and apparatus for loading radioactive seeds into brachytherapy needles. However, these devices require relatively difficult manipulations which may be time-consuming and may lead to inefficiency
U.S. Pat. Nos. 4,815,449; 4,763,642 and 6,585,633 relate to seed carriers for pre-positioning and encasing a series of seeds into a bioabsorbable material for implantation in a patient.
U.S. Pat. Nos. 4,784,116; 6,010,446 and 6,969,344 disclose specialized designs of seeds and spacers for use in providing strands of seeds spaced apart from one another by spacers. Many commercially available seeds and spacers employ one or more of these specialized designs wherein one or both of the radioactive seeds and spacers are provided with specially shaped ends adapted to mate with one another. These seed and spacer designs provide for more structurally stable seed strands, once the strands have been assembled. However, the existence of these special designs presents additional challenges in the automation of the stranding process. For example, the spacers and strands must be held for positioning and accurately aligned by the automatic stranding device for the ends to properly mate with one another when the seed and spacer are pushed together by the device.
U.S. Pat. No. 6,537,192 relates to an automated radioisotope seed loader system for implant needles. The device includes a loading station adapted to receive a replaceable cartridge preloaded with a plurality of radioactive seeds and a plurality of spacers. Seeds and spacers can be selectively ejected from the cartridge into each of a plurality of implant needles. The system may also include a computer processor as a user interface to direct operation of the loading system to load a plurality of implant needles in accordance with a predetermined dose plan.
Despite the existence of various devices for manual and automatic loading of implant needles, manual loading remains a cumbersome process that can result in undesirable exposure of users and other hospital personnel to unshielded radioisotopes. In addition, the automatic loading systems of the prior art suffer from disadvantages in allowing real-time loading in the operating room with the attendant flexibility to provide real-time treatment planning to the user during the procedure. Accordingly, it would be advantageous to provide a system for loading implant needles which would overcome one or more of these problems while improving one or more of the efficiency, flexibility and accuracy of the seed loading process.